$\begingroup$clarification question: are we talking chemically grade pure acetone, acetone from the home depot or nail polish remover with acetone? Safety always is a question of concentration.$\endgroup$
– TrishApr 13 at 8:15

6 Answers
6

Make sure the area is well-ventilated. Acetone is flammable. A buildup of acetone gas could quickly get concentrated, meaning that a single spark could lead to disaster. Using a fan is good; angle it towards an open window. This is also to prevent exposure to acetone because of its toxicity.

Be prepared to fight a fire. Should vapor ignite, you may need to fight the fire. If it is large enough, then you should clearly evacuate the area. If it appears to be small, use dry chemical powder to snuff out the fire. Alcohol foam, water spray, and/or fog may be used on slightly larger fires. Acetone is not likely to cause a large inferno to rip through the building. But there's always the chance of a small fire. Be careful.

Create a vapor chamber. This is another way to stop a potential fire from spreading. It can also reduce contamination.

Wear gloves. This can minimize any potential transfer toxic effects. However, skin exposure is unlikely to cause major issues.

Acetone is toxic, as I mentioned before, but it is not highly toxic. Exposure via the eyes and nose/mouth is the main risk. Skin effects may occur (e.g. mild irritation), but they are minor and generally arise only after long-term exposure (hence the recommendation of gloves in some cases).

Acetone exposure is only a serious problem when a person is repeatedly exposed to levels greater than 1,000 ppm (severe effects only arise at much higher levels). It seems unlikely, given a proper ventilation system, that this will be an issue

In addition to all this, basic safety precautions such as wearing a ventilator mask and goggles should definitely be taken. When working with any such chemicals with the potential for bodily harm, these should absolutely be used.

$\begingroup$@KevinMorse Fair point, in that case, and I suppose they can also protect from burns. I tend to dislike the associated clumsiness that comes with some gloves, but most don't have that issue. It's just my preference, and probably not the best one.$\endgroup$
– HDE 226868Jan 12 '16 at 22:19

1

$\begingroup$These safety instructions are incomplete. You failed to mention the need ventilation is in addition to wearing a ventilator for instance. You also left out the need to use safety equipment like goggles. In my opinion your answer should link the MSDS as a catchall for what you left unmentioned.$\endgroup$
– Emily MJan 15 '16 at 22:43

$\begingroup$@EmilyM These are basic precautions that should be obvious. Nobody in their right mind would work with acetone like this and not wear goggles or a ventilator mask, just like you wouldn't take a cake out of the oven without wearing an oven mitt. I didn't think it was necessary to include them. However, I can add them in if you feel they are not obvious.$\endgroup$
– HDE 226868Jan 15 '16 at 22:45

$\begingroup$I wasn't trying to be confrontational. But when it comes to safety recommendations assumptions aren't a good idea. People are dumb, uninformed, tired, not paying attention etc. It can't hurt to be thorough. I just want people to be safe, thus my answering the question. But since you are more likely to be the chosen answer at this point, I was hoping to convince you to make an edit for the sake of safety.$\endgroup$
– Emily MJan 15 '16 at 22:52

Contrary to what the other answers suggest, the risk of fire is not that great. An acetone "explosion" is even more unlikely, since you need a ratio of 2.5%-12.8% acetone vapor to air for that: too much acetone (as would be the case inside of your smoothing vessel) and nothing happens, too little (as would be the case inside of a badly ventilated room) and nothing happens either.

Note that even if you were working in a completely non-ventilated, ridiculously small 1m^3 room you'd still need to evaporate over half a liter of (liquid) acetone to reach that bare minimum 2.5%. In any case, well before you got into the "danger zone" the air would become unbreathable.

So, then what should you be mindful of when using acetone?

It can give you a headache. Avoid breathing the fumes and ensure adequate ventilation.

You may opt to use gloves, as skin contact should be avoided (acetone can irritate the skin and possibly be absorbed through the skin). However, limited skin contact isn't a big deal: acetone is an ingredient in some nail polish removers.

Acetone is heavier than air, so if you use a sufficiently high container fewer fumes will escape.

If somehow a fire does start, it will likely be limited to your container. Having a lid handy allows you to starve the fire of oxygen, harmlessly putting it out.

All in all, smoothing using acetone is not very dangerous. Acetone isn't suspected to be carcinogenic, though it isn't something you should be careless around either. The risk of starting a fire is small. On the other hand, solvents like MEK (used for smoothing PLA) aren't as nice by far, and should only be handled with a respirator.

No fire. Acetone is highly flammable. Avoid open flame, smoking, soldering etc. near acetone or acetone fumes. Be ready to fight a fire.

Ventilate. Acetone is very volatile so the fumes will be everywhere in the room. While breathing them should not kill you, it is certainly not good for your health. It may cause drowsiness or dizziness. It is also a good idea to close the container/jar as soon as possible and do not keep it open when not necesery.

Avoid eye contact. Acetone causes serious eye irritation. IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses if present and easy to do – continue rinsing. Seek medical help if needed.

You should also avoid skin contact; repeated exposure may cause skin dryness or cracking, but this never happens me if I wash my hand after using acetone.

Safety Advice for Acetone Handling/Usage

Please remember that you handle acetone at your own risk! By using this advice you agree to hold me harmless and not sue me as a result of using these instructions/advice. Remember that I am not a professional chemist or a lawyer (this isn't professional or legal advice)!

I encourage you to research safety precautions and risks on your own to build a personal body of knowledge. The most effective safety precaution available to you is knowledge; the brain is the most important piece of safety equipment! This listing of advice for acetone handling is generated from the highlights of a Material Safety Data Sheet (MSDS) for acetone. After reading this advice you should read an MSDS for acetone directly. It would actually be an excellent idea to find and read the MSDS for all the chemicals you use during 3D printing.

Safety Equipment

Wear safety clothing! Acetone requires that you wear protective gloves, protective eyewear, and a respirator (to protect your airway). It is also highly recommended to wear protective (ideally also chemically resistant) clothing (like a smock or an apron). These safety clothes are recommended because acetone is a toxic substance which can absorb through the skin and walls of the lungs directly. Make sure to verify the gloves are made of a substance which blocks acetone absorption, also, verify that your respirator is rated to protect against acetone (many respirators are not capable of blocking acetone due to it's volatility).

Possess, prepare and understand how to use an eyewash station, a fire blanket, a fire extinguisher (rated for chemical fires), a chemical shower/dousing system and other standard laboratory safety equipment. Posting warning signs along the entrances and exits to the work area about working with a volatile, flammable and explosive gas is also recommended.

Keep an inert absorption media readily available to cleanup spills should you accidentally fail to avoid a spill. Diatomaceous earth, silica/sand and activated charcoal are all potential absorption media. Should you have a large spill or not possess absorption media (which should not happen - always verify safety equipment is present and working before handling chemicals!) then you may also dilute the spill with water and mop up the dilute solution of acetone. No matter which method you use to cleanup a spill remember to dispose of the contaminated cleanup materials according to the requirements/laws of your local area. Do not lazily dispose of the acetone down the drain without doing research on the correct disposal methods!

Control Your Environment

Ensure proper ventilation of your workspace (ventilation is required in addition to your respirator due to explosion/fire risk). If the atmospheric concentration of acetone becomes too high the risk for fires and explosions quickly becomes unacceptable (the risk is never going to be zero working with acetone unfortunately, but minimizing it is very important). Working outside is the perfect way to insure the ventilation is adequate, although that presents it's own problems and considerations. Alternatives include using a fume hood, or even something as simple as a fan blowing air through an open window.

Eliminate any and all sources of flame or spark for a considerable area around all sources of acetone (10-15 meters minimum). Take special precautions to prevent being unknowingly contaminated with acetone (which could then be accidentally transported from the work area to a flame source using you as a carrier). Personal contamination can lead to injury if you attempt to smoke during a break or at anytime before verifying you are not contaminated. It is important to provide an ignition-free environment that extends quite far away from the immediate vicinity of the acetone because acetone can ignite a vapor trail of acetone and allow the flame to travel distances via flashing over the vapor trail. Physical isolation is the ideal solution to this dangerous problem. A policy of always closing the door to the acetone work area is an example of physical separation which would hopefully prevent this vapor trail flash-over.

Avoid acetone spills. Acetone is an excellent solvent which could easily eat away the paint on your wall or destroy the finish of your table. Spills also necessitate following special precautions for cleanup and disposal, which have already been provided earlier within this list.

Acetone Chemistry

Do not under any condition mix your acetone with chemicals without an extensive analysis and understanding of the products and the risks associated with the reaction. The following list of chemicals will create an explosive compound/mixture when reacted with acetone, so do not allow them to come into contact with acetone: hydrogen peroxide, acetic acid, nitric acid, nitric acid + sulfuric acid, chromic anydride, chromyl
chloride, nitrosyl chloride, hexachloromelamine, nitrosyl perchlorate, nitryl perchlorate, permonosulfuric acid, thiodiglycol +
hydrogen peroxide, potassium ter-butoxide, sulfur dichloride, 1-methyl-1,3-butadiene, bromoform, carbon, air, chloroform,
thitriazylperchlorate.

Should you accidentally ignite some acetone, you must take additional precautions while evacuating or while attempting to extinguish the fire. Acetone is a hydrocarbon and the reaction of burning it produces products which include carbon monoxide (CO) and carbon dioxide (CO2). Essentially, humans are incapable of detecting these gases with their senses (detectors exist to measure concentration). However, these symptoms of carbon monoxide and carbon dioxide can help alert you to the fact they are present: shortness of breath, blackness along the edges of your vision, confusion, headache, unconsciousness, coma, and finally, death. Carbon monoxide is far more dangerous than carbon dioxide because often the first symptom is unconsciousness, which prevents you from evacuating, leading to death. The dangerous of gas inhalation are substantial enough that as soon as a fire becomes medium-sized you should seriously consider evacuating the area rather than staying to extinguish the fire. It is better to lose property to the fire than to die (if you die I would guess that your property is destroyed anyway!).

Risk Analysis

Acetone is a confirmed developmental toxin for females and a suspected developmental toxin for males as well. The risk of breast milk contamination is unknown, but it is a suspected toxic contaminant. Mutagenic and tetragenic effects are not known. The result of this toxicity is that pregnant or breastfeeding women should not handle or be around acetone (due to vapors) even for short periods of time.

The risk of cancer and the carcinogenic properties for acetone are not well-defined, with some declining to classify acetone as a carcinogen and others classifying it as being carcinogenic. California, for instance, has required that acetone bear a proposition 65 warning about cancer risk.

Acetone is definitely a toxic substance, but it is not highly toxic and accidental ingestion or absorption is essentially incapable of causing severe symptoms. Small exposures to acetone (like the exposure levels likely encountered during 3D printing) are more-or-less not very harmful. However, if you do get a problematic exposure to acetone, contact a poison control center.

The LD50 ("lethal dose 50%", dose where half of subjects die) in rats is 5800 mg/kg, making the predictable (humans are often similar to rats in regards to toxicity) LD50 for an adult human similarly high. With such a high lethal dose, the predicted toxicity of acetone likely causes chronic sub-lethal damage instead of causing an acute and lethal response. If we assume an average adult human (62 kg) shares the LD50 of a rat- that human would need to consume 392 cc of acetone to reach the LD50. 392 cc is nearly equivalent to 4/10 L- meaning that there is essentially no chance the small consumption of acetone caused by working with it could poison an adult human (if our assumptions are correct).

$\begingroup$The safety precautions you describe are completely unnecessary; you are making acetone out to be far more dangerous than it actually is. Acetone does not cause cancer. Acetone it not an explosion or fire risk given the very small amounts used. The advice to not mix acetone with those specific chemicals is unlikely to be useful to a hobbyist, who will generally not have access to those chemicals. This advice is too generic to be useful to a hobbyist looking to smooth some models. While it is good to be cautious, this answer strongly overstates the risks.$\endgroup$
– Tom van der ZandenJan 16 '16 at 10:28

$\begingroup$Even if it isn't carcinogenic, Acetone can be absorbed through the skin and lungs and it is toxic to kidneys, the reproductive system, liver and skin. Acetone might cause cancer though, there is no consensus (thus why I said it may cause cancer). My list was deliberately comprehensive to insure no safety related advice was left off (I don't want to cause someone to be hurt). Personally, I agree that Acetone is not very dangerous and that using it safely is not very difficult. Please read the MSDS since you've accused me of scaremongering- my list is directly based upon that information.$\endgroup$
– Emily MJan 16 '16 at 15:20

$\begingroup$I changed the answer extensively since the comment left by Tom, so for future reader of the answer/comments, please don't assume Tom is off topic because the things he is talking about are no longer present in the form that he criticized.$\endgroup$
– Emily MJan 17 '16 at 18:54